Data center cooling energy efficiency is critical to successful operation of modern large data centers. The cooling infrastructure can account for an average of 40% of the total data center energy consumption. Adopting methods to raise the efficiency of cooling in data centers can significantly affect the cost of running them, as well as extending their life. The current trend of deploying high heat load density cabinets in data centers necessitates the use of air containment systems. Many of the modern data centers use some kind of air containment systems to achieve high cooling energy efficiency. Air containment in simple terms provides physical separation between the supplied cool air and the cabinet exhaust hot air. This separation of cold and hot air results in cooling energy savings; however, in order to observe the maximum energy savings a proper control system for cooling units is required. Typically, the cooling units get controlled based on a coupled control scheme, wherein both the fan speed and the chilled water valve/compressor speed get controlled based on a single parameter, i.e., return or supply air temperature. These type of control schemes work well for data centers without containment systems but they may not be the best way to control cooling in data centers with containment systems.
In containment systems, the cooling units and the information technology (IT) equipment are tightly connected with each other via supply air plenum and aisle containment system. Therefore, it becomes important to not only have cold air available at a proper temperature but also have the cooling airflow in the correct amount at the IT equipment inlet. Use of coupled control schemes (i.e. supply air temperature or return air temperature) in containment system does not necessarily guarantee the above conditions and almost always results in either oversupply and/or undersupply of cooling airflow. Oversupply of cooling airflow means waste in cooling energy and cooling capacity of the data center. Undersupply of cooling airflow results in IT equipment starving for cooling airflow, which could result in unreliable operation of IT equipment.
One common aspect in these decoupled control methods is the use of supply air temperature sensor to control the temperature of the air supplied by the cooling unit. Controlling the amount of air supplied to the data center however varies significantly between the different methods. Some of the ways used to control the amount of air supplied to the data center included using underfloor pressure, server or cabinet inlet temperatures, temperature difference across a containment, and containment pressure. If a data center includes only one containment system, some of these methods may succeed in reaching optimum control. Also, if a data center includes multiple containment systems that all have exactly the same heat load and airflow demand at all times, some of these methods may again succeed in reaching optimum control. However, a typical data center almost always has more than one containment system and it is rare to have the heat load and airflow demand the same for all containment systems at all times. In these situations, the existing control schemes fall short of optimum control for cooling units and result in unwanted cooling airflow bypass, which result in waste of cooling fan energy.